Serum level of cartilage oligomeric matrix protein as a screening modality for osteoarthritis among knee joint pain patients

Aim. This study aimed to evaluate the diagnostic yield of estimation of serum cartilage oligomeric matrix protein (COMP) as a screening tool for osteoarthritis (OA) among patients with knee joint pain. Methods. The study included 140 female patients with knee pain and 20 volunteers to donate blood as a control group for laboratory findings. All patients underwent full history taking, clinical examination for evaluation of pain severity using a visual analogue scale (VAS) and extent of patient mobility using mobility score (MS) and had knee anteroposterior radiographs that were scored using the Kellgren-Lawrence scoring (K-L score) system. Patients were classified according to K-L scores into: group A: pain plus no radiographic findings (K-L score=1), group B: pain plus doubtful or minimal radiographic findings (K-L score=1) and group C: pain plus radiographically determined OA (K-L score >= 2). Venous blood samples were obtained from all patients and controls for erythrocyte sedimentation rate (ESR) determination and ELISA estimation of serum COMP and high-sensitivity C-reactive protein (hsCRP) levels. Results. Group C patients had significantly higher pain scores and lower MS compared to groups A and B. Mean patients' serum COMP levels was significantly higher compared to control levels and in group C compared both to controls and to groups B and A levels with significantly higher levels in group B compared to controls and group A. However, serum COMP levels were non-significantly higher levels in group A compared to control levels. There was a positive significant correlation between serum COMP levels and body mass index (BMI), pain VAS score and radiological grade and a negative significant correlation with MS. ROC curve analysis revealed that elevated serum COMP is a sensitive predictor and high BMI is a specific predictor for the presence of OA. Serum COMP at 1097.5 ng/ml was the best cutoff point with high sensitivity (87.7\%), positive predictive value (PPV, 92.6\%) and accuracy (84.3\%) for differentiation between patient with and without OA radiological manifestations and serum COMP at 1290 ng/ml showed 100\% specificity and PPV and accuracy rate of 65.7\% for diagnosis of the presence of radiological findings of OA. Conclusion. Estimation of serum COMP level could be considered as screening modality for patients with knee pain and using cutoff point of 1097.5 ng/mL helps to define patients free of OA and cutoff of 1290 ng/ml could define patients with OA.